Antenna system



947. P. s. CARTER ANTENNA SYSTEM Filed June 3, 1942 2 Shets-Sheet 1 ew- &-

0:6 6.7 6' In WoneLE/vsrw k'rroRNEY 1947. P. s. CARTER 7 1 ANTENNA SYSTEM Filed June '3, 1942 2 Sheets-Sheet 2 fhiw earw AfroRNEY Patented Jan. 7, 1947 ANTENNA SYSTEM Philip S. Carter, Rocky Point, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application June 3, 1942, Serial No. 445,560

22 Claims. 1

The present invention relates to short wave antennas and, more particularly, to directive antenna systems for use on airplanes.

An object of the present invention is the provision of a directive antenna array having a radiation pattern free from secondary lobes or ears.

Another object of the present invention is the provision of a high gain directive antenna array.

Still another object is the provision of a multiunit antenna in which current distribution in each of the radiator units is substantially unaffected by the other units.

A further object of the present invention is the association of radiators and a transmission line in such manner that the current in each of the radiators is substantially independent of the impedance of the radiators. 7 Still a further object of the present invention is the provision of a multi-unit antenna in which the ratio between the currents in the radiator elements is controlled substantially only by the characteristic impedance of the transmission line sections connecting the elements.

Another object of the present invention is the disposition of an antenna array with respect to the body and wing structure of an airplane so as to obtain a desired directivity pattern.

The foregoing objects, and others which may appear from the following detailed description, are attained in accordance with the principles of the present invention by providing an antenna array of three coplanar dipole radiators spaced apart one quarter of the operating wavelength along a transmission line, the end dipoles being so connected to the transmission line that they are energized in phase opposition. The transmission line is energized at the locationoi the center dipole. The impedance of the transmission line is so adjusted that the current in the center dipole is twice that in the end dipoles thus obtaining a unidirectional directivity pattern. The antenna arrangement may include a plurality of arrays as set forth above arranged inparallel planes and energized in phase. The spacing between the arrays is so arranged as to obtain an optimum power ratio or power gain with respect to a single half wave dipole taken as a standard. By an appropriate arrangement of such an array with respect to the body and ring structures of an airplane a resultant directivity is obtained having a maximum response in a predetermined direction with respect to the longitudinal axis of the plane. The invention will be more fully understood by reference to the following detailed description,

which is accompanied by drawings in which Figure 1 illustrates in simplified perspective an arrangement of the present invention; Figure 2 is a schematic diagram explanatory of the principles of the present invention, while Figure 3 illustrates the resultant directivity pattern in the horizontal and vertical planes for an antenna array as shown in Figure 1; Figure 4 is a curve illustrating the relationship between the spacing of the elements of the array of Figure 1 and the power gain, while Figure 5 illustrates a proposed arrangement of the antenna array of Figure 1 with respect to a conductive sheet representing the body of an airplane and Figure 6 is a directivity pattern of the array of Figure 5, Figure '7 illustrates the arrangement of the antenna of Figure 1 with respect to a conductive sheet representing an airplane wing, while Figure 8 is'a directivity pattern illustrating the effect of the wing on the radiator.

In Figure 1 I have shown a two tier antenna array. One tier, identified by reference numeral It, consists of three half wave dipoles II, I2 and I3 side by side with a quarter wave spacing between them. A second similar tier I0, spaced from the first tier a distance S, includes three half wave dipoles Il', I2 and I3. The dipoles of tier It are connected to a transmission line I5. The transmission line I5 is transposed near its point of connection to dipole I3 so that the currents in the end radiators are in phase opposition. Of course, any other means for obtaining the phase opposing current relationship: between the end dipoles may be used. The current in the center unit I2 is arranged to be twice that of the outer units in magnitude and in phase quadrature with each of the latter. The proper amplitude relationships are determined substan tially only by the impedance of the various sections of the connecting transmission line I5. In some circumstances it may be desirable to interpose matching circuits between dipole I3 and the transmission line for adjusting the relative values of currents in dipole l2 with respect to dipoles II and [3. It should be noted that the field set up along dipole l2 by the current in dipole II is exactly out of phase with that set up by the current in dipole I3. This, of course, is equivalent to a zero value of mutual impedance between the center dipole I2 andth'e pair of dipoles II and I3. The connection of transmission line IE to. dipole units I I, I2 and I3 is similarly arranged. The two tiers Ill and ID are energized from a suitable source of high frequency energy 3 (not shown) connected to transmission line TL. The manner in which a uni-directional directivity pattern is obtained from each of the tiers of Figure 1 will be more clearly understood by reference to Figure 2.

Here, an equivalent antenna array is shown in a side view. Dipole antennas II and I3 are as before described while the center dipole has been replaced by a pair of equivalent dipoles 22 and 22'. Now, if only dipoles II and 22' are considered to be energized in phase quadratur with currents of equal amplitudes a directivepattern substantially cardioid in shape with the maximum of the cardioid in the direction of arrow M is obtained. Similarly, if only dipoles I3 and 22 are considered another cardioid having its maximum in the same direction is obtained. Now, if the center arrangement of dipoles 22 and 22 is replaced by a single dipole carrying a current equal to the sum of the currents of dipoles 22 and 22' the two separate cardioids combine in an additive relationship to obtain a resultant maximum along arrow M. It will be apparent from the following analysis that the use of a quarter wavelength transmission line between the point of connection of transmission line TL to dipole I2 and each of the dipoles II and I3 results in the currents in dipoles II and I3 being substantially independent of the impedance of antennas II and I3 and depending only upon the value of the characteristic impedance of the line TL.

If one considers transmission line TL as supplying a voltage E1. and the current of Ir. to a section of transmission line, such as one-half of transmission line 95, the section having a characteristic impedance Z and length 1, the voltage Em and current In at the remote end thereof are given by the following equations:

From these two equations it will be noted that if the length I of the line sections is an odd multiple including unity of a quarter wave the first expression to the right of the equality sign in each of the equations drops out. The current at each end of line I5, i. e., the current in dipoles H and I3, is therefore equal in magnitude to the ratio of the voltage E1. on line I5 at dipole I2 to the characteristic impedance Z0 and la s the voltage Er. by 90 in phase as indicated by the factor (-7'). The value of the impedance of the dipoles I I and I3 does not enter the relationship in any way so long as the length of the line I5 is an odd multiple including unity of a quarter wave length from feed point to load.

The current in dipole I2, which is in effect directly connected across transmission line TL is equal to the ratio of the voltage E1. to its impedance Z12 which is approximately 71 ohms resistive when tuned. By giving the characteristic impedance of the line a value of 142 ohms the currents I11, I12 and I13 in dipoles I I, I2 and I3 respectively are given by the relations:

and I12/Z11=I1z/I1s=+7'2, showing that the current in the center dipole I2 has a magnitude of twice that for the current in the outer dipoles and leads the latter currents by The impedances of dipoles II and I3 may be different from each other and difierellt from the impedance of IE without affecting their currents either in amplitude or phase. For this reason this antenna is relatively insensitive to detuning effects caused by the presence of water, ice, etc., on the dipole elements themselves.

The directivity in the vertical plane, of an antenna constructed in accordance with Figure l. is shown in Figure 3, curve 3i being the measured pattern actually determined by experimentation and test, and curve 32 being the calculated pattern. It will readily be seen that the measured and theoretical values agree very closely and in either case are quite free from secondary lobes or cars. Curve 33 of Figure 3 shows the directivity in the horizontal plane, that is, the plane parallel to the plane in which tiers It! and I0 lie. This pattern is also characterized by the substantial absence of secondary lobes or ears.

The curve in Figure 4 illustrates the effect of a variation in the spacing S between the planes in which tiers I0 and I0 lie. When the tier space S is a half wavelength the gain over that obtained with a half wave dipole is a little over 5 with the gain increasing somewhat with increasing spacing up to a value of about .78 wavelength spacing.

The body and wings of an airplane, with which the antenna of the present invention is associated, have a considerable effect on the radiation pattern of the antenna. When the antenna is mounted as shown in Figure 5, at a distance of the order of 0.4 wavelength from a conductive sheet 50 simulating the side of the body of the airplane and a distance D from the front edge of the sheet, a radiation pattern such as that shown in Figure 6 is obtained. It will be noted that the directivity pattern is somewhat sharper as the distance D increases, curve 5| of Figure 6 showing the case wherein a distance D of the order of 2 A; wavelengths is used and curve 52 where a distance D equal to 1.3 wavelengths is used.

Figure 7 shows the disposition of a single tier of the antenna structure of the present invention at a distance equal to a half wavelength from a conductive sheet 10 simulating the lower surface of the wing of an airplane, while Figure 8 shows the effect of a variation in distance X, between the center of the antenna tier and the center of curvature of the front edge of the wing. Curve II shows the directivity pattern for a distance X equal to one wavelength, while curve 12 indicates the directivity for a distance X equal to 0.2 wavelength.

For the particular application for which the antenna of the present invention was designed, the directivity shown by curve 5| of Figure 6, and curve I2 of Figure 8 very closely approximate the ideal. For example, it is required that a maximum in the horizontal plane occur at about 18 degrees with a minimum somewhere in the vicinity of 40 degrees. The spacing of 0.4 wavelength between the center of the antenna and the body of the plane fulfills these requirements quite closely, while doubling the spacing almost exactly reverses the conditions, that is, there is a minimum at 20 degrees and a maximum at'about 40 degrees. most efficient at or near the horizon and this condition occurs with the antenna placed at about 0.2 wavelength back of the front edge of the wing.

It will be noted that, particularly with respect to the directivity pattern in the vertical-plane, the results obtained appear to conflict with assump- It is also desired that the antenna be tions heretofore :commonl made as :to the effect or aconducting sheet in the field .of the antenna. It has sometimes been assumed that where :the radius of the conducting sheet from the center of the antenna is of the order .of three :wavelengths, the sheet maybe considered as an infinite plane. The .pattern actually obtained shows, however, that three wavelengths is not even an approximation of an infinite plane. There is over e30 degree variation .betweenthe maximum values obtained with a. sheet of v3 wavelengths radius and those which wouldbe expected if the sheet were actually infinite. If the sheet,

actually acted as aninfinite-planethe maximum directivity would, of course, he parallel to the planeof the sheet.

While I have particularly shown and described severalmodifications of my invention, it is to be distinctly understood that my invention is :not limited thereto but that improvements within the scope of the invention may be made.

Iclaim:

l. A directive antennasystemincludin three radiator elements arranged alongadesired line of directivity, a transmission line carrying high frequency currents coupled to said'radiator elements, the characteristic impedance of the pertions or said transmission line between each end element and the center element being twice the radiation resistance of saidcenter element.

' .2; A .directivexantenna system including three radiator elements .arrangedalong a desired line of directivity, said elements being spaced apart a distance equal to a quarter wavelength, a transmission line carrying high frequency currents coupled to said radiator elements, thecharacteristic impedance of he per tions of said'transmission line between each .end element and the center element being twice the radiation resistance of said center element.

directive antenna. system including three radiator elements arrangedalong a desired line of directivity, a transmission line carrying 'high equeucy currents coupled to said radiator elets, the characteristic impedance of the portions of said transmission line between each end element and the center element being twice the radiation resistance of said center *element'said transmission line being energized at the point of coupling of the center radiator element.

4.. A directive-antenna system including three radiator elements arranged along a desired line of directivity, said elements being spaced apart distance equal to a quarter wavelength, a transmission line carrying high frequency currents coupled to said radiator elements, the characteristic impedance of the portions of said transmission line between each end element and the center element being twice the radiation resistance of said center element, said transmission line being energized at the point of coupling of the center radiator element.

5. A directive antenna system including three radiator elements arranged along a desired line of directivity, means for coupling high frequency transducer means to the center radiator elements and quarter wave transmission line sections cou-- pling each of said end elements to said transducer means, the characteristic impedance of each of said sections being twice the radiation resistance of said center element.

6. A directive antenna system including three radiator elements arranged along a desired line of directivity, said elements being spaced apart a distance equal to a quarter wavelength, means for coupling ,rhigh .ifrequency transducer means to the center :radiator elements and transmission line sections ,coupling' each of said end elements to said transducermeansthe characteristic impedance ,ofeach.of saidsections being twice the radiation resistance :of, said center element.

521A directive antenna system in luding three radiator elements arranged along a desired line cifldiitectivity, said elements being spaced apart a distance equal to a quarter wavelength, means for coupling high frequency transducer means to the center radiator elements and quarter wave transmission line section's coupling each of said end elements to said transducer means, the characteristic impedance of each of said sections being twice the radiation resistance of said center element.

8. A directive antenna system including three radiator elements arranged along a desired line of directivity, said elements being spaced apart distance equal to a quarter wavelength, means for coupling high frequency transducer means to the center radiator elements and quarter wave transmission line sections coupling each ofsaid end elements to said transducer scans, the characteristic impedance of each of said sections bemg "twice the radiation resistance of said center element, one of said end elements being energlued in phase opposition to the other.

An antenna system including a plurality of radiator elements and a source of high frequency energy coupled thereto characterized in that the cur-rent in one of said elements is equal to the sum of the currents in the remainder, said r mainder being coupled to said one element through "transmission line sections, each having alength equal to a quarter wavelength and having a characteristic impedance equal to N times the radiation resistance of said one element where N is the number of remaining radiator elements.

10. A. radiant energy system including three radiator elements, two of said elements being coupled to transducer means by quarter wave transmission line sections and the third directly coupled thereto, the characteristic impedance of each of said sections being twice the radiation resistance of said third radiator element.

11. A radiant energy system including three radiator elements, two of said elements being coupled to transducer means by quarter Wave transmission line sections and. the third directly coupled thereto, the characteristic impedance of each of said sections being twice the radiation resistance of said third radiator element, one of of tiers of directive antenna structures, each tier being constituted in accordance with claim 7,

said tiers being arranged in parallel planes and ;energized in a similar phase relationship.

15. An antenna system including a plurality of being constituted in accordance with claim 5, said said antenna being energized in phase opposition and the center element in a quarter phase relationship with respect to each of said end elements, the plane of said antenna being arranged normal to a conductive sheet and at such distance therefrom, and said sheet extending in a direction parallel to the longitudinal axis of said antenna at such distance that th line of maxi,- mum directivity of said antenna forms an angle of the order of 20 degrees with said axis.

17. A directive antenna structure including three radiator elements arranged along a desired line of directivity, said elements being spaced apart a distance equal to one-quarter of the operating wavelength, the end elements of said system being energized in phase opposition and the center element in a quarter phase relationship with respect to each of said end elements, another similar directive antenna structure arranged parallel to said first structure and spaced therefrom by a distance of the order of .7 wavelength at the operating frequency.

18. A directive antenna structure including three radiator elements arranged along a desired line of directivity, said elements being spaced apart a distance equal to one-quarter of the operating wavelength, the end elements of said system being energized in phase opposition and the center element in a quarter phase relationship with respect to each of said end elements, another similar directive antenna structure arranged parallel to said first structure and energized in a similar phase relationship.

19. A directive antenna system comprising three radiator elements arranged along a straight line and each spaced from the adjacent one by a distance substantially equal to an odd multiple including unity of one quarter wavelength at the operating frequency, a feeder line connected directly to the center radiator element, two-conductor transmission line sections connecting said center radiator element to the other two radiator elements, said line sections having such impedances that the current in the center radiator element is substantially twice the current in either of the other two radiator elements, one of said line sections having its conductors transposed whereby the currents in the outer radiator elements are in phase opposition to each other and in a quarter phase relation with respect to the center radiator element.

26; A directive antenna structure comprising three radiator elements arranged along a straight line and each spaced from its adjacent one by an odd multiple including unity of a quarter wavelength at the operating frequency, two-conductor transmission line sections connecting the center radiator element to the other two radiator elements, said line sections having such impedances that the current in the center radiator element is substantially twice the current in either of the other two radiator elements, one of said line sections having its conductors transposed, a similar directive antenna structure arranged parallel to said first antenna structure and spaced therefrom in such manner that corresponding radiator elements and transmission line sections are similarly positioned, a transmission line section joining the two center radiator elements of both structures, and a feeder line connected to said lastline section at a location substantially midway relative to bothcenter radiator elements.

21. A directive antenna system comprising three dipole radiator elements having their centers arranged along a straight line and each spaced from the adjacent one by a distance substantially equal to an odd multiple including unity of one quarter wavelength at the operating frequency, said dipole elements being parallel to each other and arranged substantially at right angles to said straight line, a feeder line connected directly to the center radiator element, two-conductor transmission line sections conmeeting said center radiator element to the other two radiator elements, said line sections having such impedances that the current in the center radiator element i substantially twice the current in either of the other two radiator elements, one of said linesections having its conductors transposed whereby the currents in the outer radiator elements are in phase opposition to each other and in a quarter phase relation with respect to the center radiator element.

22. An antenna system including three coplanar radiator elements spaced from one another by a distance equal to an odd multiple including unity of a quarter wavelength and arranged in a straight line, a two-conductor feeder energizing the center one of said elements, transmission line sections connecting the center radiator element to the other two radiator elements, one of said transmission line sections having its conductors transposed, the lengths of each of said transmission line sections being an odd multiple including unity of a quarter wavelength from the feed point to the element being fed, said line sections having such impedances that the current in the center radiator element is substantially twice the current in either of the other two radiator elements.

PHILIP S. CARTER. 

